A novel cold-active β-D-galactosidase from the Paracoccus sp. 32d - gene cloning, purification and characterization

Abstract

Backgroundβ-D-Galactosidases (EC 3.2.1.23) catalyze the hydrolysis of terminal non-reducing β-D-galactose residues in β-D-galactosides. Cold-active β-D-galactosidases have recently become a focus of attention of researchers and dairy product manufactures owing to theirs ability to: (i) eliminate of lactose from refrigerated milk for people afflicted with lactose intolerance, (ii) convert lactose to glucose and galactose which increase the sweetness of milk and decreases its hydroscopicity, and (iii) eliminate lactose from dairy industry pollutants associated with environmental problems. Moreover, in contrast to commercially available mesophilic β-D-galactosidase from Kluyveromyces lactis the cold-active counterparts could make it possible both to reduce the risk of mesophiles contamination and save energy during the industrial process connected with lactose hydrolysis.ResultsA genomic DNA library was constructed from soil bacterium Paracoccus sp. 32d. Through screening of the genomic DNA library on LB agar plates supplemented with X-Gal, a novel gene encoding a cold-active β-D-galactosidase was isolated. The in silico analysis of the enzyme amino acid sequence revealed that the β-D-galactosidase Paracoccus sp. 32d is a novel member of Glycoside Hydrolase Family 2. However, owing to the lack of a BGal_small_N domain, the domain characteristic for the LacZ enzymes of the GH2 family, it was decided to call the enzyme under study 'BgaL'. The bgaL gene was cloned and expressed in Escherichia coli using the pBAD Expression System. The purified recombinant BgaL consists of two identical subunits with a combined molecular weight of about 160 kDa. The BgaL was optimally active at 40°C and pH 7.5. Moreover, BgaL was able to hydrolyze both lactose and o-nitrophenyl-β-D-galactopyranoside at 10°C with Km values of 2.94 and 1.17 mM and kcat values 43.23 and 71.81 s-1, respectively. One U of the recombinant BgaL would thus be capable hydrolyzing about 97% of the lactose in 1 ml of milk in 24 h at 10°C.ConclusionsA novel bgaL gene was isolated from Paracoccus sp. 32d encoded a novel cold-active β-D-galactosidase. An E. coli expression system has enabled efficient production of soluble form of BgaL Paracoccus sp. 32d. The amino acid sequence analysis of the BgaL enzyme revealed notable differences in comparison to the result of the amino acid sequences analysis of well-characterized cold-active β-D-galactosidases belonging to Glycoside Hydrolase Family 2. Finally, the enzymatic properties of Paracoccus sp. 32d β-D-galactosidase shows its potential for being applied to development of a new industrial biocatalyst for efficient lactose hydrolysis in milk.

Cloning, overexpression, purification, and characterization of a polyextremophilic β-galactosidase from the Antarctic haloarchaeon Halorubrum lacusprofundi

“…BA [53], indicating that extremophilic enzymes frequently function suboptimally under physiological conditions. The pH optimum of β-galactosidase was near neutral, similar to other family 42 β-galactosidases [16,18,26] and in contrast to family 2 β-galactosidases, which are optimally active in alkaline conditions [13,54-56]. …”

A novel cold-active β-d-galactosidase with transglycosylation activity from the Antarctic Arthrobacter sp. 32cB – Gene cloning, purification and characterization

“…The Paracoccus sp. 32d ␤-d-galactosidase was inhibited by both monosaccharides [19], whereas neither d-glucose nor d-galactose had any effect on the Arthrobacter sp. C2-2 ␤-d-galactosidase activity [14].…”

“…Two units of this enzyme (9.4 g) are capable of digesting 90% of the lactose in 1 mL of milk in 24 h at 10 • C. For comparison, 1 U of A. psychrolactophilus F2 ␤-d-galactosidase (30.0 g) hydrolyzes about 80%, while 1 U of Paracossus sp. 32d ␤-dgalactosidase (24.4 g) removes approximately 97% of lactose from 1 mL of milk under the same conditions [12,19]. The advantage of Arthrobacter sp.…”

Beta galactosidases in Arabidopsis and tomato–a mini review

“…and Paracoccus sp. [6][7][8][9]. These cold-adapted BGALs have applications in the food industry to remove lactose contaminations from heat-sensitive milk products.…”